In this series we’ll take a fresh look at resources and how they are used. We’ll go beyond natural resources like air and water to look at how efficiency in raw materials can boost the bottom line and help the environment. We’ll also examine the circular economy and design for reuse — with an eye toward honoring those resources we do have.

While changes at home can’t solve the many environmental crises we face today, they can sure help. Through this series, we’ll explore how initiatives like curbside compost pick-up, rebates on compost bins, and efficient appliances can help families reduce their impact without breaking the bank.

Despite decades -- centuries even -- of global efforts, slavery can still be found not just on the high seas, but around the world and throughout various supply chains. Through this series on forced labor, sponsored by C&A Foundation, we’ll explore many different types of bonded and forced labor and highlight industries where this practice is alive and well today.

In this series we examine how companies should respond to national controversy like police violence and the BLM movement to best support employees and how can companies work to improve equality by increasing diversity in their ranks directly.

Compost is often considered a panacea for the United States’ tremendous food waste problem. Indeed, composting is a much better option than putting spoiled food in a garbage can destined for a landfill.

PS20 Solar Power Tower by Abengoa Solar in Spain. (Photo by Tom Raftery)

The term solar thermal has been used to describe two different types of systems. One is where solar panels are used to collect heat, which is used directly as domestic or process hot water, space heating, or in some cases, air conditioning. This most basic form of solar energy utilization, called solar heating and cooling (SHC), was covered in a previous post.

The other, very different type of solar thermal system involves concentrating solar collectors that focus the sunlight, amplifying its intensity, to achieve very high temperatures that can be converted to steam to drive an otherwise conventional thermal power plant or heat engine. This is generally called concentrating solar power (CSP), which is what we are going to discuss today.

Linear concentrators are curved panels that reflect and focus the sun’s rays onto a tube that runs the length of the panel. The tube contains a fluid that heats up creating steam which is used to drive a turbine. The two main configurations are the parabolic trough type, where the tube runs along the focal line, and the linear fresnel type, which uses Fresnel lenses to collimate the reflected beam such that one receiver tube can be positioned over several mirrors. This type provides greater mobility in tracking the sun and is also less expensive.

Dish engine systems are generally smaller in scale than linear concentrators, ranging from 3-25 kW. They consist of a circular parabolic disk mirror that track the position of the sun and focus its rays onto a power conversion unit which is located along an axis extending outward from the center of the disk at the appropriate focusing distance, which is based on the curvature of the disk. The power conversion unit consists of a thermal receiver and a heat engine. The thermal receivers absorb the heat reflected from the mirror and transfer it to the heat engine. The heat engine used most commonly is the Stirling engine. Stirling engines, unlike internal combustion engines, are heated externally, and do not require the internal explosions that characterize the engines under the hoods of most cars today. Because they can be heated by any of a number of energy sources, including concentrated solar, they are far cleaner and potentially far cheaper to operate than fossil fuel powered engines. Their biggest drawback is that they are slow to respond to changes, making them unsuitable for vehicular use (except perhaps in a hybrid system where they might be used to recharge a battery).

Finally, there are the perhaps the most impressive and most scalable systems, the power towers. Power towers, also known as point-focus central receiver systems, are similar to dish/engine systems, except there is one central engine surrounded by many dishes that all focus onto it. The heated receiver produces steam, which is then used to power a conventional turbine-generator. Two 10 megawatt projects were successfully demonstrated in the U.S., back in the 90s. Spain has also deployed several units up to 20MW (pictured), the most recent using molten salt for energy storage and transfer. In 2009, eSolar launched a 5MW power tower plant, utilizing 24,000 mirrors. The DOE is currently developing a 200-megawatt molten-salt solar receiver panel for power tower technology. Two very large scale plants are also scheduled for completion next year, in the U.S.: BrightSource energy’s 392MW Ivanpah facility on the California-Nevada border, and SolarReserve’s 110MW Crescent Dunes facility, northwest of Las Vegas.

More are on the way. Saudi Arabia recently announced plans to invest $109 billion in solar power, with an eye towards generating some 41 GW, up to a third of their projected demand for the year 2030. Details are not yet known, but it will almost surely involve power tower facilities.

Unlike solar PV and solar heating and cooling, which both take advantage of the fact that the sun shines everywhere and rely on an inherently distributed model, CSP, clearly adheres to the more traditional centralized utility model, where power is transmitted over long distances from a capital-intensive central utility, where it will be sold to ratepayers.

Concentrating solar power

Pros

Renewable. No fuels required.

Non-polluting. Carbon-free except for production and transportation.

Can serve as a drop-in replacement for conventional fuels to make steam

While expensive, and far from simple, CSP holds the promise of clean energy source that can be produced at scales comparable to coal or nuclear, under the appropriate conditions. While still subject to intermittency, it has been suggested that improved thermal energy storage solutions may hold the key to the long term success of CSP.

RP Siegel, PE, is the President of Rain Mountain LLC. He is also the co-author of the eco-thriller Vapor Trails, the first in a series covering the human side of various sustainability issues including energy, food, and water in an exciting and entertaining format. Now available on Kindle.

RP Siegel, author and inventor, shines a powerful light on numerous environmental and technological topics. His work has appeared in Triple Pundit, GreenBiz, Justmeans, CSRWire, Sustainable Brands, PolicyInnovations, Social Earth, 3BL Media, ThomasNet, Huffington Post, Strategy+Business, Mechanical Engineering, and engineering.com among others . He is the co-author, with Roger Saillant, of Vapor Trails, an adventure novel that shows climate change from a human perspective. RP is a professional engineer - a prolific inventor with 52 patents and President of Rain Mountain LLC a an independent product development group. RP recently returned from Abu Dhabi where he traveled as the winner of the 2015 Sustainability Week blogging competition.Contact: bobolink52@gmail.com